Image sensing apparatus that estimates dark current and control method therefor

1. An image sensing apparatus comprising: an image sensor configured to convert an optical image of a subject into image signals by photoelectric conversion, the image sensor comprising a plurality of pixels two-dimensionally arranged, a vertical transfer unit for transferring, in a vertical direction, image signals from the plurality of pixels, and a horizontal transfer unit for transferring, in a horizontal direction, image signals transferred in the vertical direction from the vertical tranfer unit; a control unit configured to exercise control in such a way that information is acquired for estimating a magnitude of a dark current in the image sensor; any one of vertical linear noise correction processing, black subtraction processing, or normal readout processing in which neither the vertical linear noise correction processing or the black subtraction processing is carried out, is selected on the basis of the acquired information; and the vertical linear noise correction processing is carried out to correct a vertical linear noise in an image in the case of selecting the vertical linear noise correction processing, or the black subtraction processing is carried out to correct a vertical linear noise and a fixed pattern noise in an image in the case of selecting the black subtraction processing, wherein the control unit exercises control in such a way that a number of times high speed sweep is carried out for the vertical transfer unit is smaller in a case where the vertical linear noise correction processing is carried out than in a case where the black subtraction processing is carried out.

2. The image sensing apparatus according to claim 1 , wherein the control unit acquires a temperature, a shutter speed, and a sensitivity of the image sensor as the information, holds a table for relating the information to processing contents, depending on the magnitude of an estimated black current, and selects any one of the black subtraction processing, the vertical linear noise correction processing, and the normal readout processing in accordance with the table.

3. The image sensing apparatus according to claim 1 , wherein the image sensor further comprises a plurality of optical black pixels shielded from light, the control unit acquires, as the information, a first shutter speed and a first sensitivity for acquiring currently read first image signals, optical black pixel signals output from the optical black pixels from among second image signals read out from the image sensor prior to reading out the first image signals, and a second shutter speed and a second sensitivity for acquiring the second image signals, and a standard deviation for the acquired optical black pixel signals is multiplied by the ratios of the first shutter speed and the first sensitivity to the second shutter speed and the second sensitivity to estimate a magnitude of a dark current in the case of reading out the first image signals.

4. The image sensing apparatus according to claim 1 , wherein the control unit exercises control in such a way that high speed sweep is carried out for the vertical transfer unit in the normal readout processing or the black subtraction processing, and high speed sweep is not carried out for the vertical transfer unit in the vertical linear noise correction processing.

5. The image sensing apparatus according to claim 1 , wherein to carry out the vertical linear noise correction processing, empty transfer is executed in the vertical transfer unit to read out signals without transferring image signals from the pixels to the vertical transfer unit, correction data is generated for correcting a vertical linear noise on the basis of the read signals, and the correction data is subtracted from the image signals read out from the pixels.

6. The image sensing apparatus according to claim 5 , wherein in the vertical linear noise correction processing, high speed sweep for the vertical transfer unit is carried out prior to the empty transfer.

7. The image sensing apparatus according to claim 1 , wherein, to carry out the vertical linear noise correction processing, the pixels are exposed to light to acquire image signals and then shields the pixels from light to acquire black image signals, correction data is generated for correcting a vertical linear noise on the basis of the black image signals, and the correction data is subtracted from the image signals read out from the pixels.

8. A method for controlling an image sensing apparatus comprising an image sensor configured to convert an optical image of a subject into image signals by photoelectric conversion, the image sensor comprising a plurality of pixels two-dimensionally arranged, a vertical transfer unit for transferring, in a vertical direction, image signals from the plurality of pixels, and a horizontal transfer unit for transferring, in a horizontal direction, image signals transferred in the vertical direction from the vertical transfer unit, the method comprising: an acquisition step of acquiring information for estimating a magnitude of a dark current in the image sensor; a selection step of selecting, on the basis of the acquired information, any one of vertical linear noise correction processing, black subtraction processing, or normal readout processing in which neither the vertical linear noise correction processing or the black subtraction processing is carried out; a vertical linear noise correction processing step of carrying out the vertical linear noise correction processing to correct a vertical linear noise in an image if the vertical linear noise correction processing is selected in the selection step; and a black subtraction processing step of carrying out the black subtraction processing to correct a vertical linear noise and a fixed pattern noise in an image if the black subtraction processing is selected in the selection step, wherein the control unit exercises control in such a way that a number of times high speed sweep is carried out for the vertical transfer unit is smaller in a case where the vertical linear noise correction processing is carried out than in a case where the black subtraction processing is carried out.